1. Field of the Invention
The present invention relates generally to transparent carbon nitride films and more particularly to transparent carbon nitride films for use in optical or solar energy devices. It also relates to processes for making transparent carbon nitride films, and compositions of matter comprising transparent carbon nitride films.
2. Description of the Prior Art
Theoretical predictions of some of the outstanding properties of carbon nitride (C.sub.3 N.sub.4) have been made by Liu and Cohen in 245 Science 841 (1989). Because of the very short, high energy, covalent bonds in the .beta. silicon nitride (Si.sub.3 N.sub.4) structure, C.sub.3 N.sub.4 was predicted to have a higher bulk modulus and hardness than diamond. Although recent efforts have produced up to 5% of the desirable C.sub.3 N.sub.4 structure by sputter deposition at 2.5 Pa (Hailer U.S. Pat. No. 5,110,679) and 26 Pa (Morton et al., 73(1) Phys. Rev. Lett. 118 (1994)) and by pulsed laser deposition in the presence of an RF plasma at 100 Torr (Niu et al., 261 Science 334 (1993)), neither the optical properties nor the hardness of these films were reported. Both processes produced thin films which had small fractions of the C.sub.3 N.sub.4 beta structure as indicated by crystal diffraction. The crystallinity of films produced by the laser deposition process was indicated by electron diffraction measurements and the crystallinity of the films from the 2.5 Pa sputtering process was indicated by X-ray diffraction measurements. In both cases more than 95% of the material was amorphous, but other physical properties were not reported. Amorphous films of carbon and nitrogen have also been produced in a capacitively coupled rf plasma reactor at 40 Pa (Han et al., 65(9) Solid State Comm. 921 (1988)) and by RF sputtering in nitrogen at 3 Pa (Cuomo et al. 16(2) J. Vac. Sci. Tech. 299 (1979)).